1. Field of Invention
The field of art to which this invention pertains is pumping of oil and gas wells by free pistons.
2. Description of the Prior Art
External bypass piston without any frictional force against tubing walls during downward travel as in U.S. Pat. Nos. 3,304,874 and 3,319,572 do not use frictional forces available during travel down well tubing. Accordingly, such tools travel down well tubing rapidly and such apparatus strike a bottom stop with great force. To absorb such force such apparatuses are usually made very sturdily and such sturdy construction provides a heavy apparatus which then is not readily movable upwards of the tube by only small differentials in pressure. While sealing elements are provided in internal bypass pistons (U.S. Pat. No. 2,762,310) and external guides resiliently urged against well tubing string walls are known (U.S. Pat. No. 3,195,523) unless different forces are applied on upward and downward motion by seal elements to the tubing in which such plungers operate the sealing effect for upward travel is reduced and/or the force to provide change from one orientation of parts to another is so reduced as to make operation unreliable. The adaptability of prior art plungers is limited, each such apparatus being directed to a particular range of gas flows and not readily adapted to others. Also, the continued passage of a plunger in the same relation of plunger parts to the tube wears out tubing and/or plunger parts.